Education authorities in Seoul have set guidelines on temporarily closing schools amid growing public concern about the rapid spread of influenza A (H1N1) among young students.

Under the guidelines, which were made with the help of medical experts, principals at elementary and secondary schools in Seoul can decide to close a class when 10 percent of its students are confirmed to have contracted the new flu virus or 25 percent are suspected of having been infected.

Five more Koreans died from the influenza A virus over the weekend, raising the country's death toll to 40. Since the first local outbreak in May, the new flu has forced the temporary closure of schools and delayed public gatherings. More than 400 schools across the country remain closed as the new flu is highly contagious among children.

The guidelines say if more than two classes in a certain grade are closed, all students in the same year must stay at home. If more than two grades of students have their classes suspended, the school is allowed to shutdown.

Also, if a district has over 30 percent of its schools close because of the flu, all schools in the district can be closed after Seoul's top educator discusses the matter with school headmasters, parents' groups and health authorities there.

Elementary schools and kindergartens can close their doors for up to seven days, while middle and high schools can close for a maximum of five days.

However, kindergartens and schools that have students vulnerable to the virus, including disabled children, can suspend a class even when they don't meet the guidelines. "Ordinary schools as well don't need to necessarily follow the guidelines. Closure of schools is possible depending on the decision of headmasters or school boards," said an official from the Seoul Metropolitan Office of Education. Schools have also been ordered to cancel or delay any kind of social events. In addition, the education office plans to tightly supervise private cram schools or hagwon.

In the meantime, health authorities are raising their alert level for the flu virus to the highest level since the Ministry of Health, Welfare and Family Affairs adjusted it to the second-highest level last July.